Phase Decomposition in a Ti-13Nb-13Zr Alloy during Aging at 600°C

Phase decomposition in a Ti-13 mass%Nb-13 mass%Zr alloy during isothermal aging at 600°C has been investigated by means of transmission electron microscopy and Vickers hardness measurements. Specimens solution-treated at 1000°C in β phase field were quenched and aged at 600°C in (α+β) region. Beta phase was fully transformed into martensitic α' laths by quenching from 1000°C. Formation of β phase on tempered α' lath interfaces occurred during aging. Early in the stage of aging, β phase transformed into α'' martensite completely by quenching. As increasing in aging time, athermal ω phase was formed in β phase by quenching. Beta phase was stabilized by prolonged aging. Enrichment of Nb content into β phase occurred with increasing in aging time, resulting in the formations of athermal ω phase and (α+β) two-phase structure. The hardness increased with the ω phase formation in β phase, followed by the decrease of hardness due to suppression of ω phase formation induced by enrichment of Nb in β phase.